Brown dwarf

Brown dwarfs, also known as substars or semistars or orbs were astronomical objects heavier than giant planets but lighter than true stars. Most brown dwarfs had heated interiors, and experienced episodes of nuclear fusion at some point in their lives. However, brown dwarfs lacked the mass to sustain nuclear fusion, and thus did not become stars.

Properties
Brown dwarfs ranged in size from objects that massive enough to occasionally trigger fusion, to objects that were similar in appearance to gas giant planets.

L-bodies
These brown dwarfs were heavy enough to trigger some nuclear fusion. These objects were hot enough to glow with their own light. L-bodies were sometimes considered ultra-dim stars instead of brown dwarfs.

T-bodies
These brown dwarfs were lighter than L-bodies. They were far cooler, and emitted almost no visible light. They often retained heat from past nuclear fusion, and they emitted large amounts of infrared radiation. T-bodies were cool enough for more complex molecules to exist inside them.

Y-bodies
These were the smallest, lightest and coolest brown dwarfs. They appeared similar to gigantic planets, the difference being that Y-bodies had greater residual heat and some history of nuclear fusion. Some Y-bodies were cool enough explore using spacecraft.

Noteable brown dwarfs
Doornik-1142 and Goroth Beta were known brown dwarfs.